---
title: Watch filesystem changes
description: Monitor files and directories in real-time to build responsive development tools and automation workflows.
image: https://developers.cloudflare.com/dev-products-preview.png
---

> Documentation Index  
> Fetch the complete documentation index at: https://developers.cloudflare.com/sandbox/llms.txt  
> Use this file to discover all available pages before exploring further.

[Skip to content](#%5Ftop) 

# Watch filesystem changes

This guide shows you how to monitor filesystem changes in real-time using the Sandbox SDK's file watching API. File watching is useful for building development tools, automated workflows, and applications that react to file changes as they happen.

The `watch()` method returns an SSE (Server-Sent Events) stream that you consume with `parseSSEStream()`. Each event in the stream describes a filesystem change.

## Basic file watching

Start by watching a directory for any changes:

* [  JavaScript ](#tab-panel-8029)
* [  TypeScript ](#tab-panel-8030)

JavaScript

```

import { parseSSEStream } from "@cloudflare/sandbox";


const stream = await sandbox.watch("/workspace/src");


for await (const event of parseSSEStream(stream)) {

  if (event.type === "event") {

    console.log(`${event.eventType}: ${event.path}`);

    console.log(`Is directory: ${event.isDirectory}`);

  }

}


```

TypeScript

```

import { parseSSEStream } from "@cloudflare/sandbox";

import type { FileWatchSSEEvent } from "@cloudflare/sandbox";


const stream = await sandbox.watch("/workspace/src");


for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {

  if (event.type === "event") {

    console.log(`${event.eventType}: ${event.path}`);

    console.log(`Is directory: ${event.isDirectory}`);

  }

}


```

The stream emits four lifecycle event types:

* **`watching`** — Watch established, includes the `watchId`
* **`event`** — A filesystem change occurred
* **`error`** — The watch encountered an error
* **`stopped`** — The watch was stopped

Filesystem change events (`event.eventType`) include:

* **`create`** — File or directory was created
* **`modify`** — File content changed
* **`delete`** — File or directory was removed
* **`move_from`** / **`move_to`** — File or directory was moved or renamed
* **`attrib`** — File attributes changed (permissions, timestamps)

## Filter by file type

Use `include` patterns to watch only specific file types:

* [  JavaScript ](#tab-panel-8031)
* [  TypeScript ](#tab-panel-8032)

JavaScript

```

import { parseSSEStream } from "@cloudflare/sandbox";


// Only watch TypeScript and JavaScript files

const stream = await sandbox.watch("/workspace/src", {

  include: ["*.ts", "*.tsx", "*.js", "*.jsx"],

});


for await (const event of parseSSEStream(stream)) {

  if (event.type === "event") {

    console.log(`${event.eventType}: ${event.path}`);

  }

}


```

TypeScript

```

import { parseSSEStream } from "@cloudflare/sandbox";

import type { FileWatchSSEEvent } from "@cloudflare/sandbox";


// Only watch TypeScript and JavaScript files

const stream = await sandbox.watch("/workspace/src", {

  include: ["*.ts", "*.tsx", "*.js", "*.jsx"],

});


for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {

  if (event.type === "event") {

    console.log(`${event.eventType}: ${event.path}`);

  }

}


```

Common include patterns:

* `*.ts` — TypeScript files
* `*.js` — JavaScript files
* `*.json` — JSON configuration files
* `*.md` — Markdown documentation
* `package*.json` — Package files specifically

## Exclude directories

Use `exclude` patterns to skip certain directories or files:

* [  JavaScript ](#tab-panel-8033)
* [  TypeScript ](#tab-panel-8034)

JavaScript

```

import { parseSSEStream } from "@cloudflare/sandbox";


const stream = await sandbox.watch("/workspace", {

  exclude: ["node_modules", "dist", "*.log", ".git", "*.tmp"],

});


for await (const event of parseSSEStream(stream)) {

  if (event.type === "event") {

    console.log(`Change detected: ${event.path}`);

  }

}


```

TypeScript

```

import { parseSSEStream } from "@cloudflare/sandbox";

import type { FileWatchSSEEvent } from "@cloudflare/sandbox";


const stream = await sandbox.watch("/workspace", {

  exclude: ["node_modules", "dist", "*.log", ".git", "*.tmp"],

});


for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {

  if (event.type === "event") {

    console.log(`Change detected: ${event.path}`);

  }

}


```

Default exclusions

The following patterns are excluded by default: `.git`, `node_modules`, `.DS_Store`. You can override this by providing your own `exclude` array.

## Build responsive development tools

### Auto-rebuild on changes

Trigger builds automatically when source files are modified:

* [  JavaScript ](#tab-panel-8045)
* [  TypeScript ](#tab-panel-8046)

JavaScript

```

import { parseSSEStream } from "@cloudflare/sandbox";


const stream = await sandbox.watch("/workspace/src", {

  include: ["*.ts", "*.tsx"],

});


let buildInProgress = false;


for await (const event of parseSSEStream(stream)) {

  if (

    event.type === "event" &&

    event.eventType === "modify" &&

    !buildInProgress

  ) {

    buildInProgress = true;

    console.log(`File changed: ${event.path}, rebuilding...`);


    try {

      const result = await sandbox.exec("npm run build");

      if (result.success) {

        console.log("Build completed successfully");

      } else {

        console.error("Build failed:", result.stderr);

      }

    } catch (error) {

      console.error("Build error:", error);

    } finally {

      buildInProgress = false;

    }

  }

}


```

TypeScript

```

import { parseSSEStream } from "@cloudflare/sandbox";

import type { FileWatchSSEEvent } from "@cloudflare/sandbox";


const stream = await sandbox.watch("/workspace/src", {

  include: ["*.ts", "*.tsx"],

});


let buildInProgress = false;


for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {

  if (

    event.type === "event" &&

    event.eventType === "modify" &&

    !buildInProgress

  ) {

    buildInProgress = true;

    console.log(`File changed: ${event.path}, rebuilding...`);


    try {

      const result = await sandbox.exec("npm run build");

      if (result.success) {

        console.log("Build completed successfully");

      } else {

        console.error("Build failed:", result.stderr);

      }

    } catch (error) {

      console.error("Build error:", error);

    } finally {

      buildInProgress = false;

    }

  }

}


```

### Auto-run tests on change

Re-run tests when test files are modified:

* [  JavaScript ](#tab-panel-8035)
* [  TypeScript ](#tab-panel-8036)

JavaScript

```

import { parseSSEStream } from "@cloudflare/sandbox";


const stream = await sandbox.watch("/workspace/tests", {

  include: ["*.test.ts", "*.spec.ts"],

});


for await (const event of parseSSEStream(stream)) {

  if (event.type === "event" && event.eventType === "modify") {

    console.log(`Test file changed: ${event.path}`);

    const result = await sandbox.exec(`npm test -- ${event.path}`);

    console.log(result.success ? "Tests passed" : "Tests failed");

  }

}


```

TypeScript

```

import { parseSSEStream } from "@cloudflare/sandbox";

import type { FileWatchSSEEvent } from "@cloudflare/sandbox";


const stream = await sandbox.watch("/workspace/tests", {

  include: ["*.test.ts", "*.spec.ts"],

});


for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {

  if (event.type === "event" && event.eventType === "modify") {

    console.log(`Test file changed: ${event.path}`);

    const result = await sandbox.exec(`npm test -- ${event.path}`);

    console.log(result.success ? "Tests passed" : "Tests failed");

  }

}


```

### Incremental indexing

Re-index only changed files instead of rescanning an entire directory tree:

* [  JavaScript ](#tab-panel-8039)
* [  TypeScript ](#tab-panel-8040)

JavaScript

```

import { parseSSEStream } from "@cloudflare/sandbox";


const stream = await sandbox.watch("/workspace/docs", {

  include: ["*.md", "*.mdx"],

});


for await (const event of parseSSEStream(stream)) {

  if (event.type === "event") {

    switch (event.eventType) {

      case "create":

      case "modify":

        console.log(`Indexing ${event.path}...`);

        await indexFile(event.path);

        break;

      case "delete":

        console.log(`Removing ${event.path} from index...`);

        await removeFromIndex(event.path);

        break;

    }

  }

}


```

TypeScript

```

import { parseSSEStream } from "@cloudflare/sandbox";

import type { FileWatchSSEEvent } from "@cloudflare/sandbox";


const stream = await sandbox.watch("/workspace/docs", {

  include: ["*.md", "*.mdx"],

});


for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {

  if (event.type === "event") {

    switch (event.eventType) {

      case "create":

      case "modify":

        console.log(`Indexing ${event.path}...`);

        await indexFile(event.path);

        break;

      case "delete":

        console.log(`Removing ${event.path} from index...`);

        await removeFromIndex(event.path);

        break;

    }

  }

}


```

## Advanced patterns

### Process events with a helper function

Extract event processing into a reusable function that handles stream lifecycle:

* [  JavaScript ](#tab-panel-8055)
* [  TypeScript ](#tab-panel-8056)

JavaScript

```

import { parseSSEStream } from "@cloudflare/sandbox";


async function watchFiles(sandbox, path, options, handler) {

  const stream = await sandbox.watch(path, options);


  for await (const event of parseSSEStream(stream)) {

    switch (event.type) {

      case "watching":

        console.log(`Watching ${event.path}`);

        break;

      case "event":

        await handler(event.eventType, event.path, event.isDirectory);

        break;

      case "error":

        console.error(`Watch error: ${event.error}`);

        break;

      case "stopped":

        console.log(`Watch stopped: ${event.reason}`);

        return;

    }

  }

}


// Usage

await watchFiles(

  sandbox,

  "/workspace/src",

  { include: ["*.ts"] },

  async (eventType, filePath) => {

    console.log(`${eventType}: ${filePath}`);

  },

);


```

TypeScript

```

import { parseSSEStream } from "@cloudflare/sandbox";

import type { FileWatchSSEEvent } from "@cloudflare/sandbox";


async function watchFiles(

  sandbox: any,

  path: string,

  options: { include?: string[]; exclude?: string[] },

  handler: (

    eventType: string,

    filePath: string,

    isDirectory: boolean,

  ) => Promise<void>,

) {

  const stream = await sandbox.watch(path, options);


  for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {

    switch (event.type) {

      case "watching":

        console.log(`Watching ${event.path}`);

        break;

      case "event":

        await handler(event.eventType, event.path, event.isDirectory);

        break;

      case "error":

        console.error(`Watch error: ${event.error}`);

        break;

      case "stopped":

        console.log(`Watch stopped: ${event.reason}`);

        return;

    }

  }

}


// Usage

await watchFiles(

  sandbox,

  "/workspace/src",

  { include: ["*.ts"] },

  async (eventType, filePath) => {

    console.log(`${eventType}: ${filePath}`);

  },

);


```

### Debounced file operations

Avoid excessive operations by collecting changes before processing:

* [  JavaScript ](#tab-panel-8049)
* [  TypeScript ](#tab-panel-8050)

JavaScript

```

import { parseSSEStream } from "@cloudflare/sandbox";


const stream = await sandbox.watch("/workspace/src");

const changedFiles = new Set();

let debounceTimeout = null;


for await (const event of parseSSEStream(stream)) {

  if (event.type === "event") {

    changedFiles.add(event.path);


    if (debounceTimeout) {

      clearTimeout(debounceTimeout);

    }


    debounceTimeout = setTimeout(async () => {

      console.log(`Processing ${changedFiles.size} changed files...`);

      for (const filePath of changedFiles) {

        await processFile(filePath);

      }

      changedFiles.clear();

      debounceTimeout = null;

    }, 1000);

  }

}


```

TypeScript

```

import { parseSSEStream } from "@cloudflare/sandbox";

import type { FileWatchSSEEvent } from "@cloudflare/sandbox";


const stream = await sandbox.watch("/workspace/src");

const changedFiles = new Set<string>();

let debounceTimeout: ReturnType<typeof setTimeout> | null = null;


for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {

  if (event.type === "event") {

    changedFiles.add(event.path);


    if (debounceTimeout) {

      clearTimeout(debounceTimeout);

    }


    debounceTimeout = setTimeout(async () => {

      console.log(`Processing ${changedFiles.size} changed files...`);

      for (const filePath of changedFiles) {

        await processFile(filePath);

      }

      changedFiles.clear();

      debounceTimeout = null;

    }, 1000);

  }

}


```

### Watch with non-recursive mode

Watch only the top level of a directory, without descending into subdirectories:

* [  JavaScript ](#tab-panel-8037)
* [  TypeScript ](#tab-panel-8038)

JavaScript

```

import { parseSSEStream } from "@cloudflare/sandbox";


// Only watch root-level config files

const stream = await sandbox.watch("/workspace", {

  include: ["package.json", "tsconfig.json", "vite.config.ts"],

  recursive: false,

});


for await (const event of parseSSEStream(stream)) {

  if (event.type === "event") {

    console.log("Configuration changed, rebuilding project...");

    await sandbox.exec("npm run build");

  }

}


```

TypeScript

```

import { parseSSEStream } from "@cloudflare/sandbox";

import type { FileWatchSSEEvent } from "@cloudflare/sandbox";


// Only watch root-level config files

const stream = await sandbox.watch("/workspace", {

  include: ["package.json", "tsconfig.json", "vite.config.ts"],

  recursive: false,

});


for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {

  if (event.type === "event") {

    console.log("Configuration changed, rebuilding project...");

    await sandbox.exec("npm run build");

  }

}


```

## Stop a watch

The stream ends naturally when the container sleeps or shuts down. There are two ways to stop a watch early:

### Use an AbortController

Pass an `AbortSignal` to `parseSSEStream`. Aborting the signal cancels the stream reader, which propagates cleanup to the server. This is the recommended approach when you need to cancel the watch from outside the consuming loop:

* [  JavaScript ](#tab-panel-8043)
* [  TypeScript ](#tab-panel-8044)

JavaScript

```

import { parseSSEStream } from "@cloudflare/sandbox";


const stream = await sandbox.watch("/workspace/src");

const controller = new AbortController();


// Cancel after 60 seconds

setTimeout(() => controller.abort(), 60_000);


for await (const event of parseSSEStream(stream, controller.signal)) {

  if (event.type === "event") {

    console.log(`${event.eventType}: ${event.path}`);

  }

}


console.log("Watch stopped");


```

TypeScript

```

import { parseSSEStream } from "@cloudflare/sandbox";

import type { FileWatchSSEEvent } from "@cloudflare/sandbox";


const stream = await sandbox.watch("/workspace/src");

const controller = new AbortController();


// Cancel after 60 seconds

setTimeout(() => controller.abort(), 60_000);


for await (const event of parseSSEStream<FileWatchSSEEvent>(

  stream,

  controller.signal,

)) {

  if (event.type === "event") {

    console.log(`${event.eventType}: ${event.path}`);

  }

}


console.log("Watch stopped");


```

### Break out of the loop

Breaking out of the `for await` loop also cancels the stream:

* [  JavaScript ](#tab-panel-8051)
* [  TypeScript ](#tab-panel-8052)

JavaScript

```

import { parseSSEStream } from "@cloudflare/sandbox";


const stream = await sandbox.watch("/workspace/src");

let eventCount = 0;


for await (const event of parseSSEStream(stream)) {

  if (event.type === "event") {

    console.log(`${event.eventType}: ${event.path}`);

    eventCount++;


    // Stop after 100 events

    if (eventCount >= 100) {

      break; // Breaking out of the loop cancels the stream

    }

  }

}


console.log("Watch stopped");


```

TypeScript

```

import { parseSSEStream } from "@cloudflare/sandbox";

import type { FileWatchSSEEvent } from "@cloudflare/sandbox";


const stream = await sandbox.watch("/workspace/src");

let eventCount = 0;


for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {

  if (event.type === "event") {

    console.log(`${event.eventType}: ${event.path}`);

    eventCount++;


    // Stop after 100 events

    if (eventCount >= 100) {

      break; // Breaking out of the loop cancels the stream

    }

  }

}


console.log("Watch stopped");


```

## Best practices

### Use server-side filtering

Filter with `include` or `exclude` patterns rather than filtering events in JavaScript. Server-side filtering happens at the inotify level, which reduces the number of events sent over the network.

Note

`include` and `exclude` are mutually exclusive. Use one or the other, not both. If you need to watch specific file types while ignoring certain directories, use `include` patterns that match the files you want.

* [  JavaScript ](#tab-panel-8047)
* [  TypeScript ](#tab-panel-8048)

JavaScript

```

import { parseSSEStream } from "@cloudflare/sandbox";


// Efficient: filtering happens at the inotify level

const stream = await sandbox.watch("/workspace/src", {

  include: ["*.ts"],

});


// Less efficient: all events are sent and then filtered in JavaScript

const stream2 = await sandbox.watch("/workspace/src");

for await (const event of parseSSEStream(stream2)) {

  if (event.type === "event") {

    if (!event.path.endsWith(".ts")) continue;

    // Handle event

  }

}


```

TypeScript

```

import { parseSSEStream } from "@cloudflare/sandbox";

import type { FileWatchSSEEvent } from "@cloudflare/sandbox";


// Efficient: filtering happens at the inotify level

const stream = await sandbox.watch("/workspace/src", {

  include: ["*.ts"],

});


// Less efficient: all events are sent and then filtered in JavaScript

const stream2 = await sandbox.watch("/workspace/src");

for await (const event of parseSSEStream<FileWatchSSEEvent>(stream2)) {

  if (event.type === "event") {

    if (!event.path.endsWith(".ts")) continue;

    // Handle event

  }

}


```

### Handle errors in event processing

Errors in your event handler do not stop the watch stream. Wrap handler logic in `try...catch` to prevent unhandled exceptions:

* [  JavaScript ](#tab-panel-8053)
* [  TypeScript ](#tab-panel-8054)

JavaScript

```

import { parseSSEStream } from "@cloudflare/sandbox";


const stream = await sandbox.watch("/workspace/src");


for await (const event of parseSSEStream(stream)) {

  if (event.type === "event") {

    try {

      await handleFileChange(event.eventType, event.path);

    } catch (error) {

      console.error(

        `Failed to handle ${event.eventType} for ${event.path}:`,

        error,

      );

      // Continue processing events

    }

  }


  if (event.type === "error") {

    console.error("Watch error:", event.error);

  }

}


```

TypeScript

```

import { parseSSEStream } from "@cloudflare/sandbox";

import type { FileWatchSSEEvent } from "@cloudflare/sandbox";


const stream = await sandbox.watch("/workspace/src");


for await (const event of parseSSEStream<FileWatchSSEEvent>(stream)) {

  if (event.type === "event") {

    try {

      await handleFileChange(event.eventType, event.path);

    } catch (error) {

      console.error(

        `Failed to handle ${event.eventType} for ${event.path}:`,

        error,

      );

      // Continue processing events

    }

  }


  if (event.type === "error") {

    console.error("Watch error:", event.error);

  }

}


```

### Ensure directories exist before watching

Watching a non-existent path returns an error. Verify the path exists before starting a watch:

* [  JavaScript ](#tab-panel-8041)
* [  TypeScript ](#tab-panel-8042)

JavaScript

```

const watchPath = "/workspace/src";

const result = await sandbox.exists(watchPath);


if (!result.exists) {

  await sandbox.mkdir(watchPath, { recursive: true });

}


const stream = await sandbox.watch(watchPath, {

  include: ["*.ts"],

});


```

TypeScript

```

const watchPath = "/workspace/src";

const result = await sandbox.exists(watchPath);


if (!result.exists) {

  await sandbox.mkdir(watchPath, { recursive: true });

}


const stream = await sandbox.watch(watchPath, {

  include: ["*.ts"],

});


```

## Troubleshooting

### High CPU usage

If watching large directories causes performance issues:

1. Use specific `include` patterns instead of watching everything
2. Exclude large directories like `node_modules` and `dist`
3. Watch specific subdirectories instead of the entire project
4. Use `recursive: false` for shallow monitoring

### Path not found errors

All paths must exist and resolve to within `/workspace`. Relative paths are resolved from `/workspace`.

Container lifecycle

File watchers are automatically stopped when the sandbox sleeps or shuts down. If the sandbox wakes up, you must re-establish watches in your application logic.

## Related resources

* [File Watching API reference](https://developers.cloudflare.com/sandbox/api/file-watching/) — Complete API documentation and types
* [Manage files guide](https://developers.cloudflare.com/sandbox/guides/manage-files/) — File operations
* [Background processes guide](https://developers.cloudflare.com/sandbox/guides/background-processes/) — Long-running processes
* [Stream output guide](https://developers.cloudflare.com/sandbox/guides/streaming-output/) — Real-time output handling

```json
{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"/directory/","name":"Directory"}},{"@type":"ListItem","position":2,"item":{"@id":"/sandbox/","name":"Sandbox SDK"}},{"@type":"ListItem","position":3,"item":{"@id":"/sandbox/guides/","name":"How-to guides"}},{"@type":"ListItem","position":4,"item":{"@id":"/sandbox/guides/file-watching/","name":"Watch filesystem changes"}}]}
```